<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    
    <button id="btn">点击</button>
    <script>
        let timer = null
        var btn = document.getElementById('btn')
        btn.addEventListener('click',fn);
        btn.addEventListener('dblclick',fn1);
      function fn() {
        clearTimeout(timer)
        timer = setTimeout(function () {
            alert('2班');
        }, 500)
      }
      function fn1() {
        clearTimeout(timer)
        alert('4班');
      }
    </script>
</body>
</html>